Sahih Bukhari Volume 2, Book 26, Hadith Number 637.

Narated By Ibn ‘Umar : Hafsa the wife of the Prophet said, “O Allah’s Apostle! Why have the people finished their Ihram after performing ‘Umra but you have not finished your Ihram after performing ‘Umra?” He replied, “I have matted my hair and garlanded my Hadi. So I will not finish my Ihram till I have slaughtered (my Hadi).”